Aflatoxins that are natural toxins produced by fungi are known as carcinogenetic toxins and can be detected in many foods such as processed goods including peanuts, peanut butter and the like, cereals and processed goods thereof including corn, oats, buckwheat flour and the like, spices including nutmeg, white pepper and the like, and pistachio nuts. Aflatoxins are secondary metabolites produced by filamentous bacteria such as Aspergillus flavus and Aspergillus parasiticus. Aflatoxin analogs such as B1, B2, G1, G2 are known. Further, a water-soluble aflatoxin metabolite M1, found in milk from cattle having ingested aflatoxins, has been isolated and characterized. It is widely known that among them, aflatoxin B1 when orally ingested exhibits extremely high carcinogenicity.
Structural analogs such as aflatoxins B2, G1, G2 and M1 other than aflatoxin B1, although varying in carcinogenicity more or less depending on animal species and having not so strong toxicity as that of B1, are also recognized to be carcinogenic and acutely toxic in various animals.
In Japan, the concentration of aflatoxin B1 in food is regulated to be 10 ppb or less by the Food Hygiene Law, and peanuts, corn and grains wherein A. flavus or aflatoxin B1 are detected with high frequency and which are imported from countries considered as contaminated territory are particularly strictly examined. Because it is necessary that a large number of samples be rapidly dealt with, and a very small amount of aflatoxin be detected, this examination makes use of thin layer chromatography (TLC), an HPLC fluorescence method, and in confirmation examination, an LC/MS method.
When these chemical analysis methods are used, it is necessary that a sample be pulverized and then extracted with an organic solvent, followed by concentrating and purifying its extract. As a concentration and purification means, liquid-liquid partition, silica gel column chromatography and Florisil column chromatography are usually used. Further, because the concentration and purification efficacy of such chromatography is relatively low, antibody affinity column chromatography utilizing the ability of an anti-aflatoxin and the antibody to bind to aflatoxins have come to be used in order to detect a very small amount of contaminating aflatoxins. However, the existing antibody column chromatography is susceptible to some organic solvents, and is thus disadvantageously limited in that only some organic solvents are usable and that said organic solvents may be usable only at low concentrations. Although many antibodies specific to highly toxic aflatoxin B1 have been developed and published, no antibody that also reacts nearly equally to aflatoxins B2, G1, G2, and M1 has been obtained so far. Because aflatoxins B2, G1, G2, and M1 also have toxicities, including carcinogenicity, not only the content of aflatoxin B1 but also the individual contents and total amount of all aflatoxins are often subject to foreign regulations in recent years, and this tendency is estimated to increase from now. However, although there is a great need for monoclonal antibodies against aflatoxins other than B1 type, their study has been less advanced.
By way of example, previously known antibodies against aflatoxin B1 poorly recognize other types of aflatoxins. Further, some monoclonal antibodies recognize aflatoxins B1, B2 and M1 only (for example, Non-Patent Documents 1 and 2). Further still, some monoclonal antibodies recognize highly toxic B1 and G1 only, but do not recognize other types (for example, Patent Document 1). Further still, antibodies formed using B1 as a hapten may be less active toward G1; their ability to bind to G1 may be reduced by several orders of magnitude relative to B1 or B2 (Patent Document 2). On the other hand, there are monoclonal antibodies useful for detection of all aflatoxins (Patent Document 3), but the crossreactivity among aflatoxins B1, B2, G1 and G2, when compared in terms of IC50, varies greatly from ⅕ to 1/10 or less, and thus these monoclonal antibodies when used actually in detection of samples show variation among the aflatoxin analogs.
Meanwhile, a method of quantifying aflatoxin B1 by using a monoclonal antibody against aflatoxin B1 has been studied (Non-Patent Document 3), and detection of aflatoxin B1 has been conducted by ELISA (enzyme-linked immunosorbent assay) etc. However, such a method is also disadvantageous in that since the antibody is susceptible to the organic solvent and reacts poorly with other analogs, the sample must be sufficiently diluted similar to the level of dilution in antibody affinity column chromatography and therefore, depending on the content ratio of aflatoxin analogs in samples, aflatoxin B1 in some samples cannot be accurately quantified.    Patent Document 1: U.S. Pat. No. 4,835,100    Patent Document 2: JP-A 63-219394    Patent Document 3: JP-A 4-360695    Non-Patent Document 1: Candlish J. E. et al., Letters in Appl. Microbiol. 1, 57 (1985)    Non-Patent Document 2: Groopman et al., Proc. Natl. Acad. Sci. USA 81, 7728 (1984)    Non-Patent Document 3: Hertzog P. J. et al., Carcinogenesis 3: pp. 825-828 (1982)